Compensating control system



Sept. 19, 1939. J. E. HAINES COMPENSATING CONTROL SYSTEM Filed Sept. 3, 1935 2 Sheets-Sheet 1 av 6 mm E on 3 g mN m g q 3 mm @N M IN N omb 0mm QMcMo L QWQQ KOFOZ KOWWUKKEOO Patented Sept. 19, 1939 COMPEN-SATING CONTROL SYSTEM John E Haines, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Minneapolis, Minn., ware Company, a corporation of Dela- Application September 3, 1935, Serial No. 38,946

14 Claims.

The present invention relates to electrical systems of control wherein the action of a variable electrical controller upon an electrically controlled mechanism is varied by a variable electrical compensating device or adjusting device and is in part an improvement upon the system disclosed in Lewis L. Cunningham Patent No. 2,101,- 808 Dec. 7, 1937.

An object of the present invention is the provision of an electrical control system in which a variable electrical controller operates to control an electrical mechanism and in which there is a variable electrical adjusting mechanism electrically connected to the controller and electrical mechanism in a manner to vary the effect of the controller on the electrical mechanism, the

arrangement being such that the controller 211- ways maintains dominant control of the electrical mechanism even though the adjusting mechanism be in an extreme position.

Another object of the invention is the provision of means to cause equal movements of a variable electrical controller to result in substantially equal variations in the flow of current to a mechanism controlled thereby whereby, when the controller takes the form of a condition responsive variable resistance, the sensitivity of the system remains substantially constant as the controller varies such resistance from one ei'ftreme to another. I

A further object of the invention is the provision of an electrical system of control in which a current varying controller having a wide range or total differential operates an electrical mechanism upon operation of the controller over only part of its range, (in other words, the operating differential being smaller than the total differential) and providing means to vary or shift the operating differential within the total differential while maintaining the value of the operating differential substantially constant so that the sensitivity of the system remains substantially constant irrespective of where the operating differential is located in respect to the total differential.

Another object of the invention is the provision of an electrical graduated control system comprising a potentiometer type controller and one or more compensating potentiometers for varying the control action of the control potentiometer, the arrangement being such that the control potentiometer can never entirely lose command of the system even though the compensating potentiometer or potentiometers go to extreme positions.

Another object of the invention is the provision of a graduated electrical control system in which a controller having a wide total differential and a relatively narrow operating differential is arranged so that the operating differential of the controller may be shifted in respect to its total differential while maintaining the operating differential of constant value.

A further object of the invention is the pro vision of an improved effective temperature control system of the variable resistance type which is more accurate and more perfect in operation than those heretofore proposed,

Another object is the provision of a modulating or graduated effective temperature control system.

Other objects of the invention will be found in the drawings, the detailed description and the claims.

For a better understanding of the invention,

reference may be had to the following description and the accompanying drawings, in which:

Fig. 1 is a diagrammatic showing of one form of the invention wherein there is a single compensating device,

Fig. 2 is a diagramatic showing of a similar system employing a pair of compensating devices, and

Fig. 3 is a diagrammatic showing of a graduated control system employing a pair of compensating devices as well as a single controller.

Referring first to Fig. 1 of the drawings, an electrical mechanism which it is desired to control is indicated generally at i and is illustrated as comprising a balanced relay. This balanced relay l0 includes an armature ll, pivoted at l2, and provided with two legs I3 and I4. A relay coil l5 cooperates with the leg l3 and a similar relay coil I6 cooperates with the leg H. The armature ll controls a switch arm ll to which it is connected by means of a block of insulating material l8. This switch arm ll cooperates with a pair of spaced contacts l9 and between which it is disposed. It will be evident that if both relay coils i5 and iii are deenergized or are equally energized, the armature II will assume the position in which it is shown in Fig. 1 of the drawings wherein switch arm I! is intermediate contacts l9 and 20 and is disengaged from both of them. It will be further evident that if relay coil i5 is energized sufficiently more highly than the relay coil Hi, the armature II will be rotated in a clockwise direction so that switch arm i1 moves into engagement with contact [9. Similarly, if the relay coil I6 is energized sufficiently more indicated at 3|.

highly than the relay coil I5, the armature II will be rotated in a counter-clockwise direction and switch arm I1 will move into engagement with contact 26.

The respective en'erzizations of relay coils I5 and I6 are adapted to be primarily controlled by a potentiometer type of controller generally indicated at 2|. This controller includes a bellcrank 22 that is provided with an arm 23 which is adapted to be positioned by a bellows 24 that has one of its ends abutting the arm 23 and its other end secured to a support 25. The action of bellows 24 is opposed by a coiled spring 26 which has one of its ends secured to the arm 23 and its other end secured to the support 25. In the present form 01' the invention, the controller 2| takes the form of a temperature controller. The bellows 24 is therefore charged with a suitable vilatile fluid which causes expansion of bellows 24 upon a rise in the temperature to which the same is subjected. The bell-crank 22 further includes an arm 21 which takes the form of a control contact that cooperates with a control resistance 28 and is adapted'to sweep thereacross upon predetermined changes in the temperature to which the bellows 24 is subjected. The bellcrank 22 also includes a third arm 29 which is a corrector contact that cooperates with a corrector resistance 30. Both of the contacts 21 and 29 and both of the resistances 28 and 30 operate to vary the respective energizations of the relay coils I5 and I6 in a manner which will be explained hereinafter.

The respective energizations of the relay coils I5 and I6 are also adapted to be compensating control or compensator, generally This compensator 3| includes a bell-crank 32 which is provided with arms 33 and 34. The arm 33 is positioned by a bellows 35 one end of which abuts the arm 33 and the other end of which is secured to a suitable support 36. Expansion of bellows 35 is opposed by a suitable coiled spring 31 which has one of its ends secured to the arm 33 and its other end secured to the support 36. The compensator 3| is also shown herein as responsive to temperature wherefore the bellows 35 is charged with a suitable volatile fluid which expands upon temperature rise and causes arm 34 to rotate in a clockwise direction. The arm 34 takes the form of a compensating contact and its cooperates with an associated compensating resistance 38.

The balanced relay I0 may control any desired type of mechanism and is herein shown as controlling a power-failure type of relay 39 which in turn controls a motor 40. The relay 39 includes an operating or energizing coil 4| and a neutralizing or bucking coil 42, both of which cooperate in the control of an associated armature 43. The armature 43 controls switch arms 44 and 45 which respectively cooperate with associated contacts 46 and 41.

High voltage power is supplied by suitable line Wires 48 and 49 and low voltage power is supplied by a step-down transformer 50 that is provided with a high voltage primary 5| and a low voltage secondary 52. The relay coils I5 and I6, in series, are connected across the secondary 52 by Wires 53, 54. 55, 56 and 51. The compensating resistance 38 and the control resistance 28 are connected in parallel by wires 58 and 59 and these parallel connected resistances are connected in parallel with the series connected relay coils I5 and I6. through protective resistances 6D and 6|, by means of wires 62, B3, 64 and 65.

controlled by a The junction of relay coils I5 and I6 is connected to the center of corrector resistance 30 by wires 66 and 61 and is also connected to the compensating contact 34, through a resistance 68, by wires 68 and 10.

Operating of the system of Fig. 1

First, assuming that the control resistance 28 is ,the only resistance connected across the seriesconnected relay coils I5 and I6, and further assuming that the wire 61 is directly connected to the control contact 21 instead of being connected thereto through the resistance 30, it will be evident that with control contact 21 engaging the center of control resistance 28, the voltage drops across relay coils I5 and I6 will be equal and switch arm I1 will be intermediate contacts I9 and 20, as shown. Now if control contact 21 is moved along control resistance 28 towards its left-hand end, the voltage drop across relay coil I5 will be decreased and the voltage drop across relay coil I6 will increase. As the control contact 21 continues to move along control resistance 28 towards its left-hand end, the voltage drop across relay coil I5 will continue to decrease and, similarly, the voltage drop across relay coil I6 will continue to increase. However, equal movements of control contact 21 across equal amounts of the control resistance 28 will not result in equal changes in the voltage drops across relay coils I5 and I6. As the control contact 21 approaches the left-hand end of control resistance 28, the rate of change of the voltage drops across relay coils I5 and I6 for movement of control contact 21 across a predetermined amount of resistance 28 increases. As a result, the energization of relay coil I5 decreases and the energlzation of relay coil I6 increases more rapidly as the control contact 21 approaches the left-hand end of control resistance 28. In a similar manner, movement of control contact 21 along control resistance 28 towards its right-hand end causes an increase in the voltage drop across the relay coil I5 and a decrease in the voltage drop across relay coil I6. Again, however, these changes in voltage drops are not uniform for movements of control contact 21 along equal portions of resistance 28, the change increasing as the control contact 21 approaches the extreme right-hand end of control resistance 28.

The function of corrector resistance 30 and corector contact 29 is to insert more and more resistance in the circuit which connects to the junction of relay coils I5 and I6 as the control contact 21 moves away from the center of control resistance 28 in either direction. The insertion of this extra resistance in this circuit serves to prevent this increase in the rate of change of the voltage drops across relay coils I5 and I6 as the control contact 21 moves in either direction from the center of control resistance 28 and, by proper selection of the values of the control resistance 28 and the corrector resistance 30 in relation to the impedance of the coils I5 and I6, the rate of voltage change across these cells I5 and I6 can be maintained substantially constant for movements of control contact 21 along equal amounts of control resistance 28, irrespective of whether the control contact 21 be at the center of control resistance 28 or near either end thereof.

The design of the balanced relay I0 is such that only a portion of the total range of movement of control contact 21 on control resistance 28, or in other Words only a portion of the total differential of the controller 2|, is necessary to cause sumcient change in the voltage drops across relay coils l5 and I6 to move switch arm H from a position in which it engages contact 20 to a position in which it engages contact iii. In other words, the operating differential of the controller 2| is considerably smaller than its total diiferential. In actual practice, only about five per cent of the movement of the control contact 21 is required to cause a complete switching action of the balanced relay l0 wherein switch arm |1 moves from engagement with contact 28 and into engagement with contact IS.

The function of the compensating control 3| is to select the particular part of the total differential of the controller 2| at which this controller will operate the balanced relay I8. With the parts in the position shown wherein compensator contact 34 is engaging the center of compensator resistance 38, it will be evident that the control 2| will operate the balanced relay as the control contact 21 moves slightly back and forth near the center of control resistance 28. If the temperature to which the thermostat 35 responds should rise, however, compensator contact 34 moves along compensator resistance 38 towards its right-hand end which causes a lowering in the voltage drop across the relay coil l8 and an increase in the voltage drop across the relay coil I5. As a result, control contact 21 must move further along control resistance 28 towards its left-hand end as a result of a rise in temperature of the thermostatic bellows 24 in order to balance the voltage drops across the relay coils I5 and I8 so as to bring the controller 2| into control of the switching mechanism comprised by switch arm l1 and the contacts l9 and 28. In this manner, a rise in tem perature at the compensator 3| results in a raising of the control point of the controller 2|. Similarly, a fall in the temperature at the compensator 3| decreases the voltage drop across the relay coil l5 and increases the voltage drop across the relay coil IS. The control contact 21 must then move to the right of its center position and towards the right-hand end of control resistance 28 in order to operate the switching mechanism |1--|92||. In this manner, changes in the temperature to which the bellows 35 is subjected causes a shifting of the temperature at 'which the controller 2| will control the switch ing mechanism |1-| 8-20. The provision of resistance 68 is for the purpose of limiting the effect of compensator 3| upon the controller 2| in such manner that even though the compensator 3| moves to either of its extreme positions, the controller 2| can still operate switching mechanism |1-| !I#20 from one of its positions to the other of its positions Now, assuming that the controller 2| responds to the temperature of a space to be controlled and has a total differential of 10 ranging from 75 F. to 85 F., and that the compensator 3| responds to outdoor temperatures and has a total differential of 25 ranging from 75 F. to 100 F. With the parts in the position shown, the outdoor temperature is substantiall 875 F., and the inside, or space temperature, is substantially 80 F. With the parts in the positionshown, the motor 48, which may be a compressor motor, is energized to reduce the temperature of the room or space by a circuit as follows: Line wire 49, wire 15, switch arm 45, contact 41, wire 18, compressor motor 40 and wire 11 to line wire 48. Operation of compressor motor M will lower the temperature of the room or space. Control contact 21 will therefore move along control resistance 28 towards its right-hand end. This results in a lowering of the voltage drop across the relay coil l8 and an increase in the voltage drop across the relay coil l5. Armature N then rotates in clockwise direction and switch arm |1 moves towards contact l9. When the switch arm |1 engages contact IS, the energizing coil 4| of the relay 38 is energized by a circuit as follows: Secondary 52, wire 51, wire 58, wire 18, contact 8, switch arm l1, wire 19, energizing coil 4|, wire 88, wire 8|, and wire 53 to the other side of secondary 82. Energization of energizing coil 4| attracts armature 43 and moves switch arm 44 into engagement with contact 46 and switch arm moves out of engagement with contact 41. Movement of switch arm from engagement with contact 41 interrupts the energizing circuit for compressor motor 40. Engagement of switch arm 44 with contact 48 establishes a holding circuit for energizing coil 4| which is independent of the switch arm l1 and the contact l8. This holding circuit is as follows: Secondary 52, wire 51, wire 82, switch arm 44, contact 48, wire 83, energizing coil 4|, wire 80, wire 8|, and wire 53 to the other side of secondary 52. The armature 43 therefore remains in its attracted position even after switch arm |1 engages discontact l8.

With the compressor motor 48 now deenergized, the temperature of the room or space will soon begin to increase. Such increase in the space temperature is accompanied by movement of control contact 21 along control resistance 28 towards its left-hand end. This causes a decrease in the voltage drop across relay coil I5 and an increase in the voltage drop across the relay coil l6 so that armature rotates in a counter-clockwise direction. When this rise in room temperature has been sufficient, the switch arm i1 will engage contact-'28 whereupon an energizing circuit for the neutralizing coil 42 is established'as follows: Secondary 52, wire 51, wire 82, switch arm 44, contact 46, wire 83, wire 19, switch arm |1, contact 20, wire 84, neutralizing coil 42, wire 8|, and wire 53 to the other side of secondary 52. Such energization of the neutralizing coil 42 creates a magnetic flux equal to and opposing that produced by the energizing coil 4| whereupon there is no longer any attractive force operating upon armature 43 and the same returns to the position shown in Fig. 1 of th drawings by gravity. This causes separation of switch arm 44 from contact 48 and movement of switch arm 45 into engagement with contact 41. Separation of switch arm 44 and contact 46 not only interrupts the holding circuit for energizing coil 4| but interrupts the energizing circuit for neutralizing coil 42 so that there is still no attractive force operating on armature 43 and the same will remain in its new position. Engagement of switch arm 45 with contact 41 energizes compressor motor 48 by the circuit,

traced above whereupon the room or space being controlled is again cooled. The relay 38 will then remain in the position shown until the temperature of the room or space has again decreased sufiiciently to move switch arm |1,engagement with contact l9 whereupon the above described operation will be repeated.

In this manner, for any given outdoor tempera ture, the controller will operate the balanced relay iii) room or space temperature within such predetermined narrow range of temperature. Upon a change in the outdoor temperature, the operating range of the controller 2I will be shifted to a new temperature as pointed out above. As previously pointed out, movement of compensator contact 34 towards the left end of compensating resistance 88 operates to reduce the voltage drop across the relay coil I5. As a result, the room temperature must fall to a lower degree before the voltage drop across relay coil I will be increased over the voltage drop across the relay coil I8 sufficient to cause movement of switch arm I! into engagement with contact I8. In this manner, as the outdoor temperature drops, the temperature which is maintained within the room or space is also lowered. Similarly, a rise in outdoor temperature will be accompanied by 9. raising of the control point of the controller 2I so that a higher temperature within the space will be maintained. By selecting the range of the controller 2| at a difierentialand the range of the compensator 8| at a 25 diiferential, it will be apparent that the temperature maintained in the room or space being controlled will be raised at a slower rate than the outdoor temperature rise whereby a variable differential is maintained between the indoor and outdoor temperatures. By reason of the provision of resistance 88, the controller 2I will still be operative to move the switch arm I1 into engagement with either of the contacts I8 or 28 even though the compensator 8| goes to either of its extreme positions. In addition, the provision of the corrector resistance 38 provides for equal operating differentials of the controller 2| in controlling the switching mechanism I1-I8-28,-irrespective of whether the control point of the controller 2I be near iIs low, its middle or its high end.

Now referring to Fig. 2 of the drawings, it will be seen that the system of Fig. 2 corresponds to the system of Fig. 1 except that two compensators are utilized instead of a single compensator. Those parts of Fig. 2 which correspond with similar parts of Fig. 1 have applied thereto the same reference characters as utilized in Fig. 1.

The additional compensator comprises an apparatus generally indicated at 85 and includes a bell-crank 88 having arms 81 and 88. A humidity.

responsive element 88, herein shown as formed of a plurality of strands of hair, has-one of its ends secured to the arm 81 and its other end secured to a suitable support 88. A tension spring 8| has one of its ends secured to the arm 81 and its other end secured to a suitable support 82 and serves to maintain the humidity responsive element 89 under proper tension. The arm 88 is a compensator contact and it cooperates with a compensator resistance 88, the arrangement being such that compensator contact 88 moves along compensator resistance 93 towards its left-hand end'upon an increase in the value of the relative humidity to which the humidity responsive element 88 responds. This compensating resistance 83 is connected in parallel with the compensating resistance 38, as well as in parallel with the control res stance 28, by means of the wires 58 and 58 and two additional wires 84 and 85. The compensator contact 88 is connected to the junction of relay coils I5 andIG through a resistance 88 by wires 91, 98, 89 and 86. It will therefore be evident that the compensator 85 is connected to the system in the same manner as the compensator 8|.

In the system of Fig. 2 therefore, the control point of the controller 2I is not only shifted by reason of the compensator II but also by reaing controlled causes a decrease in the voltage drop across the relay coil I5 and an increase in the voltage drop across the relay coil I8 wherefore the temperature of the space must be lowered in order to cause movement of switch arm II into engagement with contact I8 so as to bring about in stopping of the compressor motor 88. Similarly, upon a decrease in the relative humidity of the space, the compensator 85 raises the control point of controller 2| so that a higher temperature is maintained in the space. In this manner, a sulr stantially constant effective temperture is maintained within the space for any given outdoor temperature and the eifective temperatureis raised as the outdoor temperature rises, but at a slower rate, whereby a variable diilerential is maintained between the outdoor dry bulb temperature and the indoor effective temperature. I In the system of Fig. 2, the resistance 88 which is associated with the compensator contact 88 permits dominating control by the controller 2I even though the compensator 85 moves to either of its extreme positions. In view of the explanation of the system of Fig. 1, it is thought that the detailed manner in which the system of Fig. 2 operates will now be apparent.

Turning now to Fig. 3 of the drawings, a graduated system of compensating control is shown in distinction to the on and of! systems of compensated control shown in Figs. 1 and 2. The system of Fig. 3 includes a balanced relay designated generally at I88 which includes an armature III that is pivoted at I82. The armsture I8I is provided with legs I88 and I88 with which relay coils I85 and I85 respectively cooperate. Auxiliary windings I81 and I88 of relatively small power also cooperate with the respective legs I88 and I84. The armature I8I controls a switch arm I88, the switch arm I88 being connected to the armature I8I through the medium of a piece of insulating material I I8. This switch arm I88 is disposed between a pair of cooperating contacts III and H2 so that the switch comprised by the switch armI88 and contacts III and H2 comprises a single pole, double throw switch.

The energizations of relay coils I85 and I88 are adapted to be maintained substantially constant at all times by means which will be described hereinafter. Unbalancing of the energizations of the relay coils I85 and I88 is accomplished by means of a controller and two compensators which correspond in their details to the controller 2| and compensators 8I and 85 of the system of Fig. 2 wherefore the reference characters of Fig. 2 applying to the controller and compensators have been applied to the controller and compensators of Fig. 3.

- Low voltage power is. supplied to the system of Fig. 3 by a step-down transformer II5 that is provided with a high voltage primary H8 and a low voltage secondary III. The relay coils I85 and I86, in series, are connected across the secondary III by wires H8, H8, I28, I2I, I22 and I23. The control resistance 28 and the corrector resistances 38 and 82 are all connected in parallel with each other and in parallel with the series connected relay coils I85 and I88 by wires I24, I25, I26, I21, I23 and I29. It will therefore be seen that all three of these resistances 23, 33 and 93 and the series-connected relay coils I and I06 are all connected in parallel with each other and across the secondary II1.

Rebalancing of the energ'izations of relay coils I05 and I06 is accomplished by a balancing potentiometer generally indicated at I which comprises a balancing resistance I3I and a balancing contact I32.. This balancing resistance I3I is also connected across the secondary II1 by wires II3, I33, I34 and I23.

The junction of relay coils I05 and I06 is connected to the center of corrector resistance 30 and is further connected to the compensator contacts 33 and 34 and to .the balancing contact I32 thr'ough suitable adjustable rheostats. Wires I35 and I36 comprise the connections between the junction of relay coils I05 and I 06 and the center of corrector resistance 30. The circuit from the junction of relay coils I05 and I06 to the compensator contacts 33 and 34 is as follows: Wire I35 and wire I31, where the circuit branches, one part going by wire I33, a rheostat I59, and a wire I40 to the compensator contact 33, whereas the other portion goes by way of wire I, a rheostat I42, and a wire I43 to the compensator contact 34. The junction of relay coils I05 and I06 is connected to the balancing contact I32 through a rheostat I 44 by wire I35 and wires I45 and I46.

The balancing potentiometer I30 is controlled by the final or main operating shaft I 01' a motor mechanism generally indicated at I5I. In

,the specific example shown, the balancing contact I32 is connected to this main operating shaft I50. The 'main operating shaft is connected to a rotor shaft I52 by means of suitable reduction gearing I53. Secured to rotor shaft I52 is a pair of motor rotors I54 and I55 which respectively cooperate with'field windings I56 and I51. The main operating shaft I50 may control any desired type of apparatus or mechanism and is herein shown as controlling a valve 158 which may, for example, control the flow of cooling medium to a suitable cooling coifi The connections between the valve I53 and the main operating shaft I50 comprise a pinion I59 vsecured to the main operating shaft I50, this pinion I59 in turn cooperating with a rack I60 that is secured to the valve stem I6I 'of the valve I53.

Operation of the system of Fig. 8

With the parts in the position shown, the control contact 21, the compensator contacts 30 and 34 and the balancing contact I32 are all engaging the centers of their respective resistances 28, 93, 33 and I3I and the corrector contact 29 is engaging the center 'of corrector resistance 30 to which the wire I36 is connected so that no part of the corrector resistance 30 is in the circuit. Under these conditions, the relay coils I05 and I06 are equally energized and the switch arm I09 i intermediate the contacts III and H2,

Assuming that the controller 2| responds to the temperature of a space to be controlled and that the compensator 85 responds to the relative humidity of such space whereas the compensator 3I responds to outdoor temperatures, all as explained in connection with Fig. 2, then, with the parts in the position shown, the valve I53 is half-open and just sufficient cooling fluid is being allowed to flow to the cooling apparatus to maintain the temperature of the space constant. If the space temperature should rise. somewhat so contact is that control contact 21 moves along control resistance 23 towards its left-hand end, then the voltage drop across the relay coil I05 decreases and the voltage drop across the relay coil I06 increases. This causes counter-clockwise rotation of armature IOI and movement of switch arm I09 towards contact III. When the temperature rise is sufllcient to bring switch arm I09 into engagement with contact III, field winding I51 and the auxiliary winding I03, in series, are energized by a circuit as follows: Secondary II1, wire II3, wire II9, wire I65, switch arm I09, contact III, wire I66, auxiliary winding I03, wire I61, a limit switch I63, wire I69, field winding I51, wire I10, wire I22, and wire I23 to the other side of secondary I I1. Energization of the auxiliary winding I03 causes an additional attractive force to be applied to armature IOI, tending to rotate the same in counter-clockwise direction, so that switch arm I09 is held firmly in engagement with contact III. Energization of field winding I51 causes rotation of main operating shaft I50 in a clockwise direction as viewed from the left so that the rack I60 is raised to open the valve I53 more widely and the balancing contact I32 moves upwardly along balancing resistance I3I. Such movement of balancing contact I32 along the balancing resistance I3I reduces the voltage drop across the relay coil I06 and increases the voltage drop across the relay coil I05. This causes clockwise movement of armature IM or tends to cause such movement and when this rotative force is great enough, switch arm I09 disengages contact III. When this occurs, the auxiliary winding I03 and the field winding I51 are both deenergized whereupon further rotation of main operating shaft I50 ceases. This deenergization of auxiliary winding I03 removes the additional attractive force on armature IOI, tending to rotate the same in counter-clockwise direction, whereupon the same rotates a small amount furtherin clockwise direction so as to move switch arm I09 a substantial distance from contact II I. The valve I53 has now been moved to a more wide open position such as should be sufficient to maintain the space temperature at its new value.

On the other hand, if the space temperature should fall, control contact 21 will move along control resistance 23 towards its right-hand end whereby the voltage drop across relay coil I06 will be lowered and the voltage drop across relay coil I05 will be increased. Armature IOI there'- fore rotates in a clockwise direction and switch arm I09 moves towards contact I I2. When this fall in space temperature has been sufficient, switch arm I09 engages contact II2 whereupon auxiliary winding I 01 and field winding I56, in series, are energized as follows: Secondary II1, wire II3,-wire II9, wire I65, switch arm I09, wire II2, wire I1I, auxiliary winding I01, wire I12, 9. limit switch I13, wire I14, field winding I56, wire I10, wire I22 and wire I23 to the other side of secondary II1. Main operating shaft I50 is now rotated in a counter-clockwise direction as viewed from the left whereupon rack I50 moves downwardly to partially close the valve I58 and the balancing contact I32 moves downwardly along balancing resistance I3I. Energization of the auxiliary winding I01 causes a further attractive force on armature IOI tending to move switch arm I09 towards contact II2 whereby a good firm maintained between these parts. Movement of balancing contact I32 downwardly along balancing resistance I 3I reduces the voltage drop across relay coil I05 and increases the voltage drop across relay coil I06. When the voltage drops across these relay coils have thus been changed sulhciently, switch arm I09 disengages contact I I2 to interrupt the circuit through auxiliary winding I0"! and field Winding I56. Further rotation of main operating shaft I50 thereupon ceases. Deenergization of the auxiliary winding I01 permits further movement of switch arm I09 away from contact II2 to insure a good clean break. The valve I58 has now been closed somewhat to reduce the supply of cooling medium to the room or space being controlled whereby the temperature thereof should not lower any further.

In this manner, so long as the relative humidity of the space being controlled and so long as the outdoor temperature both remain constant, the controller 2| operates to variably position valve I58 to maintain the temperature of the space within a portion of the total range of operation of the controller 2|. The fluctuation in room temperature will be relatively small and with the parts in the position shown, the temperature of the.room or space will be maintained at substantially F. The provision of the corrector contact 29 and corrector resistance 30 provide for equal movements of valve I58 for equal move ments of control contact 2'! irrespective of the position in respect to control resistance 28 as pointed out in connection with the systems of Figs. 1 and 2.

If the relative humidity of the space should now increase, compensator contact 88 will move along compensator resistance 93 towards its lefthand end whereupon the voltage drop across relay coil |05 will be reduced and the voltage drop across relay coil I06 will be increased. As a result, for any given position of control contact 21, the balancing contact I32 must move further towards the upper end of balancing resistance |3| in order to maintain the energizations of relay coils I 05 and I05 sufiiciently equal to maintain switch arm I09 intermediate contacts III and H2. Therefore, as the relative humidity in the space increases, more cooling fluid will pass to the cooling apparatus for any given temperature within the space whereby the temperature of the space maintained by the controller 2| will tend to lower. In this manner, the control or operating range of controller 2| is shifted upon changes in the space relative humidity whereby the eifect ive temperature is maintained substantially constant. The opposite action takes place, of course, on a lowering in the relative humidity in the space.

In a similar manner, a decrease in the outdoor temperature also reduces the voltage drop across relay I05 and increases the voltage drop across relay coil I06 so that balancing contact I32 again must move upwardly along balancing resistance |3I to a greater extent for any given position of the controller 2| and compensator whereby more cooling will be eifected. This likewise tends to reduce the temperature maintained in the space, the opposite action taking place upon a rise in outdoor temperature. In this manner, a substantially constant efifective temperature is maintained in the space by permitting the relative humidity to vary as it may and varying the dry bulb temperature thereof. In addition, the standard of effective temperature maintained in the space is raised as the outdoor temperature rises but at a slower rate so that avariable differential is maintained between the outside dry bulb temperature and the inside effective temperature.

The rheostat I44, which is in circuit with the balancing contact I32, provides for extra resistance in the balancing circuit for relay coils I05 and I06 so that a larger movement of the balancing contact I32 is required to rebalance the energizations of relay coils I05 and I06 than the movement of control contact 21 which causes such unbalance. As a result, the operating dlfierential of the controller 2| can be made less than its total differential and the value of this operating diiierential willdepend upon the adjustment of rheostat I44. The rheostats I39 and I42, which are in circuit with the compensators I5 and 3|, prevent complete short-circuiting of either of the relay coils I05 and I06 by either of iese compensators and makes it possible for the controller 2| to have dominating control of the apparatus even though one or both of the compensators go to either of its extreme positions. As stated before, the corrector resistance 30 operates to maintain the operating differential oi! the controller 2| substantially constant irrespective of whether this controller be operating near the center or near either end. The limit switches I68 and H3 can be actuated in any of the usual manners by the movements of the motor mechanism ISI '50 as to limit the extreme movements of main operating shaft I50 in either direction.

While compensation of the indoor temperature maintained within a space to be controlled has been disclosed wherein the indoor temperature is raised as the outdoor temperature rises, but at a slower rate, so as to give a variable differential between indoor and outdoor temperature and while some of the systems additionally provide for compensation according to changes of relative humidity in the space, it is to be understood that the systems disclosed herein are of general utility wherever it is desired to compensate the value of one condition which is maintained by a control mechanism in accordance with changes in another condition. For instance, if it were desired to raise the temperature of water in a boiler as the outdoor temperature decreased, the controller 2| of Fig. 1 would be made to respond to boiler water temperature and the compensator 3| would be made to respond to outdoor temperature. The end connections of the compensating resistance 38 would then be reversed from what is shown in Fig. 1 so that the control point of the controller 2| would be raised as the outdoor temperature decreased. It would also, of course, be necessary to select controllers and compensators having the proper total ranges or diflerentials in order to give the type of compensation desired.

As a practical example, the control resistance 28, the compensating resistance 38, the compensating resistance 39 and the balancing resistance |3| each have a resistance of 135 ohms. The total resistance of corrector resistance 30 is 70 ohms, one-half of this resistance being on each side of the wire which is connected to its center. The value of the protective resistances 60 and GI utilized in the systems of Figs. 1 and 2 is 25 ohms each. The value of the resistance 68 of Fig. l is 45 ohms However, where two compensators are used, as in the system of Fig. 2, the value of the resistances 68 and 96 is ohms each. The rheostais I39, I42 and I44 utilized in the system of Fig. 3 may be adjusted from a minimum of 25 ohms to a maximum of 300 ohms.

This minimum adjustment prevents complete 75 short-circuting of either of relay coils I05 or I06 upon extreme movements of balancing contact I32, or extreme movements of either compensator. The combined impedance of the seriesconnected relay coils I05 and I06 is approximately ohms where the current supply has a frequency of 60 'cycles. The low voltage secondary II! is 20 volts.

In adapting any of the systems of Figs. 1, 2 and 3 to any desired type of compensating control, the values of the various controlling and compensating resistances are always maintained equal and the instrument is so constructed as to cause the contact thereof to completely traverse such controlling or compensating resistance upon the desired change in the particular condition or conditions being used to control and compensate. It will be obvious that many minor modifications may be made in these systems without departing from the novel features of the present invention, and I am to be limited thereforecnly in accordance with the scope of the appended claims.

I claim as my invention:

1. In an electrical control system, in combination, a pair of normally equally energized series connected electrical coils, a control potentiometer having a control resistance and a control contact movable in respect to each other, connections connecting said control resistance in parallel with said series connected coils and said control contact intermediate said coils, means to vary the positions of said control re sistance and control contact in respect to each other, current varying means controlled by said position varying means operable to insert resistance between said control contact and the Junction of said coils whenever the control contact is not engaging the center of said control resistance, and a device to be controlled operated by said electrical coils.

2. In an electrical control system,- in combination, a pair of normally equally energized series connected electrical coils, a control potentiometer having a-control resistance and a control contact movable in respect to each other, connections connecting said control resistance in parallel with said series connected coils and said control contact intermediate said coils, means to vary the positions of said control resistance and control contact in respect to each other, current varying means controlled by said position varying means operable to insert resistance between said control contact and the junction of said coils whenever the cont-rol.contact is not engaging the center of said control resistance, a device to be controlled operated by said electrical coils, and adjustableresistance means electrically connected to said control potentiometer and said coils operative upon adjustment to vary the effect of said control potentiometer upon said coils.

3. In an electrical control system, in combination, a pair of normally equally energized series connected electrical coils, a control potentiometer having a control resistance and a control contact movable in respect to each other, connections connecting said control resistance in parallel with said series connected coils and said control contact intermediate said coils, means to vary the positions of said control resistance and control contact in respect to each other, current varying means controlled by said position varying means operable to insert resistance between said control contact and the junction of said coils whenever the control contact is not engaging the center of said control resistance, a device to be controlled 4. In an electrical control system, in cornbination, a pair of normally equally energized series connected electrical coils, a control potentiometer having a control resistance and a control ccntact movable in respect to each other, connections connecting said control resistance in parallel with said series connected coils and said contrcl contact intermediate said coils, means to vary the positions of said control resistance and control contact in respect to each other whereby to vary the respective energizations of said series connected coils, current varying means controlled by said position varying means operable to insert resistance between said control contact and the junction of said coils whenever the control contact is not engaging the center of said control resistance, motor means controlled by said coils, a device to be positioned operated by said motor means, and a balancing potentiometer electrically connected to said series connected coils operated by said motor means in a manner to maintain the energizations of said series connected coils substantially equal. 5. In an electrical control system, in combination, a pair of normally equally energised series connected electrical coils. acontrol potentiometer having a control resistance and a control contact movable in respect to each other, connections connecting said control resistance in parallel with said series connected coils and said control contact intermediate said coils, means to vary the positions 01 said control resistance and control contact in respect to each other, current varying means controlled by said position varying means operable to insert resistance between said control contact and the junction of said coils whenever the control contact is not engaging the center of said control resistance, a balancing potentiometer comprising a balancing resistance and a balancing contact, a device to be positioned. motor means controlled by said coils in control of said balancing potentiometer-1nd device, connections connecting the balancing resistance in parallel with said control resistance, a resistance. and connections connecting hid balm '00Ii tact to the junction of said coils through said resistance. 6. In an electrical control system, in combinaticn, a pair of electrical coils connected in series across a source of power, a control potentiometer and a balancing potentiometer connected in parallel with said series conected coils and each having substantially equal resistance, connections between the junction of said coils and the confacts of said potentiometers, a variable resistance having a minimum setting in the connection between said junction and the contact of the balancing potentiometer, said minimum setting of the variable resistance preventing complete shortcircuiting of either coil upon extreme positions of said balancing potentiometer and the resistance also determining the amount of movement of said control potentiometer required to cause a complete extreme position of said balancing potentiometer to substantially rebalance the energizations of said coils, a device to be positioned,

means controlled by said coils to operate said balancing potentiometer and position said device, and variable resistance means operable to increase its resistance upon movement of the control potentiometer out of its center position in either direction by said operating means, said variable resistance means being included in the circuit between the contact of said control po tentiometer and the junction of said coils.

'7. In an electrical control system, in combination, a pair of electromagnetic coils connected in series across a source of power, switching means controlled by said coils upon a predetermined change in their respective energizations, means to be controlled operated by said switching means, a control potentiometer including a control resistance connected in parallel with said series connected coils and a control contact connected to the junction of said coils, said control potentiometer being capable of changing the respective energizations of said coils more than said predetermined change required to cause operation of said switching means, adjustable means associated with said potentiometer to determine the portion of its range of movement which will cause said predetermined change in the energizations of said coils, and means operable with said potentiometer to require substantially equal movements thereof throughout its range of movement to result in said predetermined change in the energization of said coils.

8. A temperature control system of the class described, comprising, in combination, means to change the temperature of a space, means in control of said temperature changing means including a pair of electromagnetic coils connected in series across a source of power, a controller responsive to space temperature and having a range of response within which it is desired to vary the space temperature upon fluctuations in outdoor temperature, said controller comprising a resistance and a cooperating contact movable in respect to each other upon change in the space temperature, an outdoor temperature responsive controller having a range of response equal to the range of outdoor temperatures for which it is desired to vary the space temperature, said second controller comprising a resistance and a cooperating contact movable in respect to each other, electrical connections connecting one end of each resistance to one end of the series connected coils and connecting the other ends of said resistances to the other end of said series connected coils, a third resistance, connections connecting the movable contact of said second controller intermediate the series connected coils through said third resistance, a fourth resistance having an intermediate point connected intermediate said series connected coils, and a contact operated by said first controller which engages said intermediate point of the fourth resistance only when the movable contact of the first controller engages the center of its associated resistance.

9. In an electrical compensated control system, in combination, motor means movable in two directions for performing a control function, a pair of normally balanced electrical coils connected in series across a source of power, means controlled by said series connected coils upon unbalancing thereof for causing movement of the motor means in one direction or the other depending upon the direction of unbalance of the series connected coils, a control potentiometer including a control resistance and a control contact, means for relatively adjusting the control contact with respect to the control resistance throughout a complete range of adjustment, a balancing potentiometer including a balancing resistance and a balancing contact, means operated by said motor means for relatively adjusting the balancing contact with respect to the balancing resistance in accordance with the direction and extent of movement of the motor means, connections for connecting the control resistance and the balancing resistance in parallel to the series connected coils and the control contact and the balancing contact to the junction of the series connected coils whereby the motor means is moved in accordance with the adjustment of the control potentiometer, resistance means located in the connections between the balancing potentiometer and the series con nected coils for desensitizing the controlling ac tion of the balancing potentiometer whereby the motor means may be moved to either extreme position upon adjustment of the control potentiometer through a relatively small operative range of adjustment within the complete range of adjustment, a compensating potentiometer including a compensating resistance and a compensating contact, means for relatively adjusting the compensating contact with respect to the compensating resistance, connections for connecting the compensating resistance in parallel with the series connected coils and the compensating contact to the junction of the series connected coils whereby the motor means is also moved in accordance with the adjustment of the compensating potentiometer, and resistance means-located in said last mentioned connections for always allowing the control potentiometer to control the current flow through the coils even though the compensating potentiometer is adjusted to an extreme position and for desensitizing the controlling action of the compensating potentiometer whereby the relatively small operative range of adjustment of the control potentiometer is shifted within the complete range of adjustment thereof in accordance with the adjustment of the compensating potentiometer.

10. In an electrical compensated control sys-, tem, in combination, motor means movable in two directions for performing a control function, a pair of normally balanced electrical coils connected in series across a source of power, means controlled by said series connected coils upon unbalancing thereof for causing movement of the motor means in one direction or the other depending upon the direction of unbalance oi the series connected coils, a control potentiometer including a control resistance and a control contact, means for relatively adjusting the control contact with respect to the control resistance throughout a complete range of adjustment, a balancing potentiometer including a balancing resistance and a balancing contact, means operated by said motor means for relatively adjusting the balancing contact with respect to the balancing resistance in accordance with the direction and extent of movement of the motor means, connections for connecting the control resistance and the balancing resistance in parallel to the series connected coils and the control contact and the balancing contactto the junction of the series connected coils whereby the motor means is moved in accordance with the adjustment of the control potentiometer, resistance means located in the connections between the balancing potentiometer and the series connected coils for desensitizing the controlling action of the balancing potentiometer whereby the motor means may be moved toeither extreme position upon adjustment of the control potentiometer through a relatively small operative range of adjustment within the complete range of adjustment, a compensating potentiometer including a compensating resistance and a compensating contact, means for relatively adjusting the compensating contact with respect to the compensating resistance, connections for connecting the compensating resistance in parallel with the series connectedcoils and the compensating contact to the junction of the series connected coils whereby the motor means is also moved in accordance with the adjustment of the compensating potentiometer, resistance means located in said last mentioned connections for always allowing the control potentiometer to control the current flow through the coils even though the compensating potentiometer is adjusted to an extreme position and for desensitizing the controlling action of the compensating potentiometer whereby the rela tively small operative range of adjustment of the control potentiometer is shifted within the complete range of adjustment thereof in accordance with the adjustment of the compensating potentiometer, and means for adding and subtracting resistance in the connection between the control contact and the junction of the series connected coils upon adjustment of the control potentiometer to maintain the relatively small operative range of adjustment thereof substantially constant.

11. In an electrical compensated control system, in combination, a pair of normally balanced electrical coils connected in series across a source of power, mechanism controlled by said normally balanced series connected coils and placed in operation upon a predetermined unbalance in one direction and out of operation upon a predetermined unbalance in the oppositedirection, a control potentiometer including control resistance and a control contact, means for relatively adjusting the control contact with respect to the control resistance throughout a complete range of adjustment, connections for connecting the control resistance in parallel with the series connected coils and the control contact to the junction of the series connected coils, the arrangement being such that the series connected coils are unbalanced in one direction to place the mechanism in operation and are unbalanced in the opposite direction to place-the mechanism out of operation upon adjustment of the control potentiometer through a relatively small operative range of adjustment within the. complete range of adjustment, a compensating potentiometer including a compensating resistance and a compensating contact, connections for connecting the compensating resistance in parallel with the series connected coils and e compensating contact to the junction of the series connected coils whereby the series connected coils are also controlled by the compensating potentiometer, and resistance means included in said last mentioned connections for always allowing thecontrol potentiometer to control the current flow through the coils even though the. compensating potentiometer is adjusted to an extreme position and for desensitizing the controlling action of the compensating potentiometer whereby the relatively small operative range of adjustment of the control potentiometer is shifted within the complete range of adjustment thereof in accordance with the adjustment of the compensating potentiometer.

12. In an electrical compensated control system, in combination, a pair of normally balanced electrical coils connected in series across a source of power, mechanism controlled by said normally balanced series connected coils and placed in operation upon a predetermined unbalance in one direction and out of operation upon a predetermined unbalance in the opposite direction, a control potentiometer including control resistance and a control contact, means for relatively adustlng the control contact with respect to the control resistance throughout a complete range of ad ustment, connections for connecting the control resistance in parallel with the series connected coils and the control contact to the junction of the series connected coils, the arrangement being such that the series connected coils are unbalanced in one direction to place the mechanism in operation and are unbalanced in the opposite direction to place the mechanism out of operation upon adjustment of the control potentiometer through a relatively small operative range of adjustment within the complete range of adjustment, 9, compensating potentiometer including a compensating resistance and a compensating contact, connections for connecting the compensating resistance in parallel with the series connected coils and the compensating contact to the junction of the series connected coils whereby the series connected coils are also controlled by the compensating potentiometer, resistance means included in said last mentioned connections for always allowing the control potentiometer to control the current flow through the coils even though the compensating potentiometer is adjusted to an extreme position and for desensitizing the controlling action of the compensating potentiometer whereby the relatively small operative range of adjustment of the control potentiometer is shifted within the complete range of adjustment thereof in accordance with the adjustment of the compensating potentiometer, and means for adding and subtracting resistance in the connection between the control contact and the junction of the series connected coils upon adjustment of the control potentiometer to maintain the relatively small operative range of adjustment thereof substantially constant.

13. A temperature control system for a space, comprising, in combination, means to change the temperature of a space, means including electrical means in control of the temperature changing means, a control potentiometer, means responsive to space temperature for adjusting the control potentiometer through a complete range of adjustment in accordance with permissible variations in space temperature, means including connections between the electrical means and the control potentiometer to control the temperature changing means upon adjustment of the control potentiometer through a relatively small operative range of adjustment within the complete range of adjustment thereof, a compensating potentiometer, means responsive to space relative humidity for adjusting the compensating potentiometer in accordance with variations in space relative humidity, connections between the compensating potentiometer and the electrical means whereby the tempera ture changing means is also controlled by space relative humidity, and resistance means associated with said compensating potentiometer for always allowing the control potentiometer to contrql said electrical means and for desensitizing the controlling action of the compensating potentiometer whereby the relatively small operative range of adjustment of the control potentiometer is shifted withinthe complete range of adjustment thereof in accordance with the adjustment of the compensating potentiometer to maintain desired temperatures within the space that vary in accordance with changes in space relative humidity.

14 A temperature control system for a space, comprising, in combination, means to change the temperature of a space, means including electrical means in control of the temperature changing means, a control potentiometer, means responsive to space temperature for adjusting the control potentiometer through a complete range of adjustment in accordance with permissible variations in space temperature, means including connections between the electrical means and the control potentiometer to control the temperature changing means upon adjustment of the control potentiometer through 9.

7 range of adjustment oi the control potentiometer is shifted within the complete range of adjustment thereof in accordance with the adjustment of the compensating potentiometer to maintain desired temperatures within the space 20 that vary in accordance with changes in outside temperatue.

JOHN E HAINES. 

